Various molding processes exist to form a variety of molded articles. For example, injection molding, blow molding, compression molding, vacuum molding, and the like, have been used in many industries for fabrication of various molded articles. The molds and molded articles can be formed from a number of materials and in a variety of configurations. Historically, a mold has been a costly piece of manufacturing equipment and has typically been suited to fabricate a single design of the molded article. In such an arrangement, any change to the design of the molded article generally would require the creation of a new mold. This arrangement then required a costly retooling anytime a change was made to the molded article design.
In addition, any change to the molded article design, or to the mold itself, would often require considerable time because the entire mold would need to be rebuilt. Further still, a given mold can only be used for the specific design of the molded article for which it was built. This would require multiple complete molds to fabricate multiple parts or multiple designs (e.g., parts of different sizes, different styles, etc., all typically require a new and different mold). These conventional mold arrangements are costly and generally limit the variations available within a production run of a given molded article.
In some applications, a method for producing multiple, dimensionally accurate, and functional prototypes of an article involves the use of polymeric molds in an injection molding system. Although the primary focus of the following description relates to tooling for injection molding, those skilled in the art will recognize that other molding systems, such as blow molding, would be suitable for producing prototypes. Injection molding is an intermittent, cyclic process in which particles of polymeric material are heated until molten. The molten material is then forced into a closed mold in which it solidifies to form a desired article. The manner in which the molten material solidifies depends on the type of injected material. Thermoplastic materials harden upon cooling while thermosetting materials solidify by the addition of heat. Injection molding systems typically include mixing and melting sections, a means for injecting the molten mass, and a molding section.
Molds within injection molding systems contain a cavity, or female section, which represents a reverse image of an outer peripheral surface of a desired article, and a core, or male section, which represents the inner details of the article. The cavity and core sections of an injection mold are supported in mold fixtures, or shoes, that are in turn supported on a top part sometimes referred to as the cope, and a bottom part sometimes referred to as the drag. The cope and the drag are clamped together under pressure. One or more openings, or “sprues,” are provided in portions of the mold sections to introduce the molten mass of polymeric material into the cavities of the mold. A mold design must also provide venting to allow for the escape of air and other gases as the molten material is introduced into the mold.
The material of choice for mold construction must be capable of withstanding the injection molding operation. Sufficient temperature and pressure must be developed within the tool to ensure the molded product will reflect the resin manufacturer's performance specifications. An approximate plastic pressure applied to the resin during injection and packing will vary from about 1200 psi to about 20,000 psi.
The molds used in an injection molding process may be designed using a computer-aided design software package that analyzes the configuration of the desired article. The software program thereafter calculates a reverse image of the desired article and allows the incorporation of desired venting, cooling, and ejection channels. Prototypes are molded from a number of different polymeric materials. The selected molding material corresponds to the type of material to be used on the final article. As a result of using the same type of molding material, the user can produce a functional prototype. A functional prototype means that the resulting prototype has substantially the same properties, such as weight, density, feel, and flexibility, as the desired final article. A functional prototype can be subjected to a battery of performance tests as well as being visually inspected for accuracy. The ability to subject the resulting prototypes to destructive testing is a significant advantage over systems that produce only one prototype per production cycle. Examples of commonly used polymeric materials include polyolefins such as polypropylene, styrenics such as acrylonitrile-butadiene-styrene copolymer (ABS), polycarbonate, acetal etc.
Unfortunately, injection molding is extremely hard on molds due to the abrasiveness of the injected materials, the temperatures, and the pressures, so a mold or mold insert produced from the plastic materials typically used in an additive manufacturing process is not able to withstand the conditions of typical injection molding of plastics for large numbers of articles produced.
The present disclosure is directed to addressing one or more of the problems set forth above and/or other problems associated with rapid prototyping of tooling for an injection molding operation.